With the development of a radio communication service, a demand for a bandwidth of a radio communication system is becoming higher and higher, which leads to an increasing shortage of available frequency band resources. Therefore, how to improve a utilization efficiency of a frequency band becomes a key issue in radio communication research. Technologies that can effectively improve the utilization efficiency of the frequency band include: multiple access, signal detection, modulation, and channel encoding. Furthermore, a multi-antenna system (MAS) becomes increasingly important for a radio communication technology.
In a cellular mobile communication system, the MAS may be set in a base station of each cellular cell. The MAS may include multiple physical antennas to transmit a signal. The physical antenna is also known as an antenna array element. In the multi-antenna system, multiple antenna array elements and signal processing units are organically combined, and thus transmission and reception can be adaptively optimized according to the change of a channel environment. A communication service provided by the multi-antenna system not only may be a unicast signal that is transmitted through a dedicated channel to a particular mobile terminal, but also may be a broadcast multicast signal that is transmitted through a common channel to all mobile terminals. The broadcast multicast signal may be, such as a multimedia broadcast multicast service (MBMS) signal, system information transmitted through a broadcast channel, a reference signal transmitted through a synchronization channel, and a pilot, a paging, and a common control message that are transmitted through a Forward Access Channel (FACH).
For the transmission of a unicast signal, a technology such as beam forming or precoding may be provided for the multi-antenna system to implement the transmission of the unicast signal. For example, a Smart Antennas (SA) system, also known as an antenna array system (AAS), is a kind of multi-antenna system. Spacing between antenna array elements of the SA is smaller than a correlation distance of a channel. In the SA system, the beam forming may be implemented by a signal correlation between the antenna array elements. Furthermore, in the SA, a narrow beam with a high gain is adaptively directed at a mobile terminal in communication, and a null is adjusted to align with an interference direction, so as to minimize the interference with other users.
For an SA system, the beam forming may concentrate energy of a transmission signal on a quite narrow beam and generate a gain in a specified direction. Therefore, if M physical antennas are used to achieve the same coverage in a dedicated channel as that of a single omni-directional antenna, the transmission power needed on each antenna is only 1/M2 of that on the single antenna. M is a natural number that is at least equal to 2. Thus, signal power of each physical antenna can be amplified respectively by using a low power amplifier.
However, the prior art has the following defects: an amplifier with high power is needed to amplify the signal of the physical antenna in order to obtain omni-directional cell coverage in a common channel, which significantly increases a device cost. Furthermore, when a space-time-frequency coding technology is adopted in the SA system, configuration of an antenna array needs to be strictly limited and a hardware structure of a receiver also needs to be fixed, which lead to poor extensibility.